The primary purpose of these studies is to gain a better understanding of the relationship between metabolism and transport in renal tubules. In this regard, we have developed recently a unique combination of established investigative techniques. Microfluorometry is used to monitor changes in the redox level of mitochondrial NAD in various preparations of transporting renal epithelia which allow direct and simultaneous measurements of transport events. The application of two independent techniques (microfluorometry and measurements of transport) to specific areas of the kidney will provide the first direct correlations between changes in renal transport and metabolism. Parallel studies will be performed to establish the biochemical basis of the fluorometric signals by direct measurements of ATP, ADP, oxygen consumption and spectrophotometric assay of cytochrome redox levels. These parallel studies will provide the factual and conceptual framework upon which the microfluorometric data may be interpreted. Four preparations will be used: 1) frog kidney, isolated and perfused in vitro, 2) rabbit renal cortical tubules, separated and with open lumens, 3) rabbit proximal tubules, isolated and perfused in vitro, and 4) isolated mitochondria from the rabbit kidney.